<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>demo</title>
    <style>
        .demo{
            background-color: tan;
        }
    </style>
</head>
<body>
<button id="btn">点我创建一个输入框</button>
<script type="text/javascript">
    const btn =document.getElementById('btn')
    btn.onclick =()=>{
        const input = document.createElement('input')
        input.className='demo'
        input.value=99
        input.onclick=()=>{alert(1)}

        document.body.appendChild(input)
        input.focus()//获取焦点
        input.parentElement.style.backgroundColor="blue"
    }

</script>
</body>
</html>